This project will create two large parallel series of historical U.S. census microdata. The first is a redesigned Integrated Public Use Microdata Series (IPUMS) incorporating Census 2000 and American Community Surveys. The second is a restricted-use microdata archive containing 1.4 billion records from the censuses of 1940 to 2000. The two series will be developed simultaneously using the same software, methodology, and documentation. The IPUMS is a compatible series of large census microdata samples spanning the period from 1850 to 1990. The new restricted-use archive is the product of a Census Bureau initiative to harmonize all of the Bureau's decennial microdata. The Bureau has decided to use the IPUMS design for these internal files and will make them accessible through the Census Bureau Research Data Centers. The project will collaborate with the Census Bureau to create variable coding schemes incorporating all detail in the restricted files, and will apply the same codes to the public data. Redesign of certain variables will also be necessary to accommodate Census 2000 and the ACS. Capitalizing on new federal investment in historical census geography, the project will create fully compatible geographic identifiers for the restricted files. For the public data, it will reduce existing geographic incompatibilities, provide electronic boundary files for mapping, and create tools to attach aggregate contextual data to individual-level records. Close similarity of the public and restricted data will enable researchers to design their analyses with publicly accessible data and limit expensive time in a Research Data Center. Public-use test data sets will be developed to mimic the unique aspects of the restricted files, allowing researchers to test research designs, demonstrate their feasibility, and minimize research costs. To reduce maintenance costs and ensure preservation, all documentation will be converted to new archival metadata standards. Version control software will allow scholars to replicate data extracts used in published research. Use of open-source software standards will allow both the Census Bureau and the Inter-university Consortium for Political and Social Research (ICPSR) to install, disseminate, and maintain IPUMS-format data.